I use drush to execute cron on my Drupal sites. After upgrading drush from version 5 to version 8, I started receiving empty emails from cron each time drush was executed. Checked my cron entries and everything looked fine. Researched a whole bunch on the Internet. Couldn’t find much of anything about empty emails related to drush so I redirected the output to a log. Sure enough, even with the –quiet option, drush cron still outputs a blank line.

I ran into two issues when setting up Let’s Encrypt SSL certificates on two of my servers - permission issues for Exim and the certbot cron job supplied by the package doesn’t handle the renew very well for nginx, exim or dovecot.
Resolving Exim’s Permission Problems 1. Create a new group. I named it sslcerts. Add the exim user to that group. If you’re not using Debian, adjust the user in the command below.

I ran into a problem with NGINX failing to start on boot/reboot on my Debian 8 (Jessie) server. After reviewing what seemed like a hundred sites to try to find a fix, I stumbled across one solution that worked, but was incredibly inelegant. This was to add:
RestartSec=30s Restart=on-failure to nginx.service in the [Service] section using the override.conf. It worked but didn't fix the underlying problem.
A quick look using `journalctl -u nginx` showed that the service was failing because the IPv6 address hadn't been assigned to the network adaptor yet.

merge-ngx-conf.pl is a perl script used to assemble a set of nginx configuration files for one site. It has a number of options. See the bitbucket page or the help documentation in the script itself.
In its simplest form, it’s called by issuing this command:
merge-ngx-conf.pl /path/sites-available/filename
The output is an assembled nginx configuration file with all the includes inserted. Using nginx.conf and domain.conf (or just domain.conf depending on the options selected), the script iterates through the include directives in the files and inserts the text from the referenced file.